Connection improvements

[wowawiwa]

Reformulated:

When the SSE connection is interrupted (e.g. because the user switched tab, or networking issues).
Then the BE ends up dropping the session after a while. If the FE doesn't notice it, it could show the user wrong information.
For example, the FE shows the Room, but updates aren't received.

As long as the SSE connection is not doing errors, the session cannot have been lost.
But on error: It could be because of networking error. In this case, the session has not been lost: Only the SSE must be reopen.
Or it could be that the session has been Lost.
But the SSE api doesn't seem to allow knowing that. Thus, we must find a way for the FE to ask the BE if the session is still there.

Original:

• EventSource connection has TTL 3 minutes. If the client goes in a tunnel for more than that, the client will fail reconnecting, he should hello again. This isn't handled. (How to catch this in the EventSource thing?).
• Allow UI to send "close session" (case where the user closes the session on purpose).

[wowawiwa]

@abustany please confirm if it fits to what we discussed.

FE generates a new SessionID on App loading. It represents a distinct journey of the user on the App.

It sends it as parameter in the initial and subsequent hello (sessionId, together with clientId, secret).

hello responds with the eventsUrl and newSession: boolean which states if it has a session corresponding to the SessionID or not. If it doesn't have any, it creates one. Otherwise, it "touches" the existing session.

The intent is for the FE to be able to confirm if it is still in sync with the BE after a connection interruption.